Polyacrylates with improved biodegradability

ABSTRACT

A hydrophilic polymer with improved biodegradability and particular usefulness in detergent compositions contains units derived by polymerization from at least one monomers A bearing a carboxylic acid function or an equivalent function, units derived by polymerization from at least one monomers B bearing an electron-rich group or a function capable of introducing an electron-rich group into the main chain, and, optionally, units derived by polymerization from at least one monomers C which is copolymerizable with A and B, but is different from A and B. Examples of suitable monomers as monomers A include maleic anhydride, acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid, and the salts thereof. Examples of suitable monomers as monomers B include butadiene, isoprene, chloroprene, dimethylbutadiene, cyclohexadiene, butadienecarboxylic acid, butadienedicarboxylic acid, acetylene, acetylenecarboxylic acid and acetylenedicarboxylic acid. Suitable monomers as monomers C include vinyl, acrylic and styrene monomers and derivatives thereof.

The invention relates to biodegradable polymers and in particular topolyacrylates with improved biodegradability.

The polyacrylates of the invention can be used in various applicationsand in particular in detergent compositions.

In general, detergent compositions involve a certain number of chemicalproducts. These should be biodegradable so as not to harm theenvironment. Detergent compositions and cleaning agents conventionallycontain phosphates. These are highly effective and relatively non-toxic,but cause eutrophization of natural aquatic media.

Phosphates have been partially replaced in detergent formulations bypolymers such as polyacrylic acides or copolymers based on acrylic acidand on maleic anhydride.

Although the polyacrylates currently used do not pose this problem,their absence of rapid biodegradability causes an accumulation in thenatural environment (Swift, Polymer Degradation and Stability, 45,215-231, 1994).

No toxicity associated a priori with these polymers is known, but theirlong-term effect is uncertain, and this uncertainty has contributedtowards the instigation of numerous research studies intended to improvetheir biodegradability.

It is clearly established that hydrophilic polymers, such as polyvinylalcohol, are rapidly degraded by microorganisms (Macromol. Chem. Phys.196, 3437, 1995). It is also known that polyacrylic acids with anaverage molecular weight of less than 1000 have better biodegradabilitythan their higher homologs (Swift, Ecological Assessment of Polymer 15,291-306, 1997).

EP 0 497 611 discloses the preparation of biodegradable terpolymers andof compositions containing them. These terpolymers are based on vinylacetate, acrylic acid and maleic anhydride. They have weight-averagemolecular masses of less than 20 000.

U.S. Pat. No. 5,318,719 discloses a novel class of biodegradablematerials based on the grafting of polymers containing acidic functionsonto a polyoxyalkylene-based biodegradable support.

Other studies indicate that chains comprising hetero atoms are morereadily degraded than carbon-based chains. Thus, U.S. Pat. No. 4,923,941discloses biodegradable copolymers containing carboxylic acid functionsand heterocycles, as well as the detergent compositions containing them.

The Applicant has now found that the degradability of the polymersdescribed above can be improved by inserting sites of fragility into themain chain. These sites will be rapidly broken by the microorganisms ofthe natural environment, to give acrylic blocks that are small enough inmass to be readily biodegradable.

The Applicant has found that the insertion of electron-rich centres,such as double bonds, into an acrylic chain makes the acrylic chain morefragile with respect to microorganisms and thus improves itsbiodegradability.

It is moreover well known that although carbon-based chains are highlychemically and biologically resistant, this is true only in the case ofsaturated chains. The reason for this is that if a chain comprisesmultiple bonds (electron-rich), these readily oxidizable and chemicallyreactive bonds will constitute the first sites of cleavage of themolecule. Among the multiple bonds, carbon-carbon double bonds appear tobe the ones most readily usable.

The invention relates to hydrophilic polymers with improvedbiodegradability, in particular polyacrylates containing readilyoxidizable electron-rich sites.

The polymers of the invention contain:

-   -   from 70% to 99% by weight of units derived by polymerization        from at least one monomers A bearing a carboxylic acid function        or an equivalent function,    -   from 1% to 30% by weight of units derived by polymerization from        at least one monomers B bearing an electron-rich group or a        function capable of introducing an electron-rich group into the        main chain,    -   from 0% to 29% by weight of units derived by polymerization from        at least one monomers C which is copolymerizable with A and B,        but is different from A and B.

They can also contain a chain-limiting transfer agent.

Irrespective of the monomers A, B and C, the final polymer should remainhydrophilic.

The monomers A is chosen from the group consisting of monomers bearingat least one carboxylic acid and derivatives thereof, such as acid saltsand anhydrides. As a non-limiting guide, mention may be made of maleicanhydride, acrylic acid, methacrylic acid, itaconic acid, fumaric acidand maleic acid, and the salts thereof.

The monomers A which is preferred according to the invention is acrylicacid.

The monomers B is chosen from the group consisting of:

-   -   monomers bearing two conjugated double bonds, such as butadiene,        isoprene, chloroprene, dimethyl-butadiene, cyclohexadiene,        butadienecarboxylic acid and butadienedicarboxylic acid, and    -   monomers bearing a triple bond, such as acetylene,        acetylenecarboxylic acid and acetylenedicarboxylic acid.

The preferred monomers B of the invention is isoprene.

The monomers C, which is different from A and B, is chosen from thegroup containing monomers that are copolymerizable with A and B, such asvinyl, acrylic and styrene monomers, and derivatives thereof.

The distribution in the final polymer of the fragile sites provided bythe monomers B depends both on the intrinsic relative reactivity of thevarious monomers present and on the ratio of the relative concentrationsof monomers A, monomers B and optionally other monomers C.

The polymers of the invention may be linear or branched. They may alsobe partially crosslinked.

Polyacrylic acids partially neutralized and crosslinked with the aid ofa molecule containing at least two functions that are reactive withcarboxylic acids and containing the fragile sites described aboveconstitute a perfect example of branched polymers with improvedbiodegradability according to the invention.

Among these polymers, mention may be made of the products generally usedas aqueous-liquid absorbing agents and often referred to assuperabsorbents (SAPs).

The polymers of the invention may be obtained by the jointpolymerization of:

-   -   70% to 99% by weight of at least one monomers A,    -   1 to 30% by weight of at least one monomers B, and    -   0% to 29% by weight of at least one monomers C.

The monomers A, B and C are those described above.

The polymerization may be carried out in solution in an organic solventor in the presence of water. As a guide, these two modes of synthesisare described for the production of a linear product:

-   -   in the presence of organic solvent:

The polymerization takes place in tetrahydrofuran (THF). When thepolymerization is performed batchwise, the monomers mixture isintroduced into the solvent along with the initiator(azobis-isobutyronitrile, AIBN) and, where appropriate, a transfer agentsuch as thioglycolic acid (TGA) or another thiol.

After degassing and placing under nitrogen, the reaction is initiated byraising the temperature to 70° C.

The monomers A, B and C, if used, may be introduced continuously withthe aid of a metering pump into the reactor throughout the reaction,with the aim of better distributing the functional monomers throughoutthe chain and of thus obtaining a polymer of more uniform composition.

After reaction and concentration of the THF on a rotary evaporator, thepolymer is precipitated and dried in an oven under vacuum.

-   -   in the presence of water:

The monomers mixture, the initiator (potassium persulphate, K₂S₂O₈) and,where appropriate, a transfer agent such as thioglycolic acid (TGA) oranother thiol, are introduced into the water.

After degassing and placing under nitrogen, the reaction is initiated byraising the temperature to 70 or 80° C.

After polymerization, the product is recovered by evaporation and dryingunder vacuum.

The biodegradability of the products obtained is examined in thefollowing way:

-   -   Evaluation of the biodegradability    -   Oxidative prescreening

This test is intended to evaluate the sensitivity of the new sequencesto the action of oxidative degradation of microbial enzymes.

Given that the oxidative enzymes are neither easy to use norcommercially available, the test method described below uses metalcomplexes, which are analogs of oxidative enzymes, and in particularTPEN N,N,N′,N′ tetramethylpyridine-1,2-ethylenediamine orN,N,N′,N′-tetrakis(2-pyridylmethyl)ethane-1,2-diamine.

The reaction conditions used for the degradability test are as follows:

Polymers to be tested 1 mg/ml (test volume = 10 ml) TPEN combined withFe(III) 0.05 mM Free TPEN 0.5 mM H₂O₂ 100 mM pH 7 Temperature 50° C.Time 4 h

The evaluation of the level of degradation obtained is made by liquidchromatography under the following conditions:

Column Tosohaas TSK 3000 Eluent 0.1 M H₃CCOONa Flow rate 0.5 ml/min.Injection 25 μl after 0.22μ filtration Detection Differentialrefractometer Data acquisition Dionex Peaknet

The column is calibrated by means of polyacrylate standards (PolymerLaboratories).

The degradability of the polymer under the test conditions is measuredby the shift of the peak observed in liquid chromatography towards lowermolecular masses.

This shift is quantified by means of a degradability index I₁₀₀₀ definedin the following way:

Initial mass of the polymer Mi Final mass of the polymer Mr Number ofcleavages Nc Initial degree of polymerization ${Dp} = \frac{Mi}{Mmono}$

-   -   with M_(mono): “average” mass of the monomers    -   degradability index: $I_{1000} = {\frac{Nc}{Dp} \times 1000}$        i.e.:        $I_{1000} = {\left( {\frac{Mi}{Mr} - 1} \right) \times \frac{Mmono}{Mi} \times 1000}$        Microbiological Degradation

Experimental Cultures

Candida tropicalis cultures are prepared on a liquid medium comprisingmalt extract (20 g.l⁻¹) and incubated at 30° C. with axial agitation for48 hours.

These cultures are centrifuged at 18 000 rpm for 15 minutes and thepellet is washed with 0.1 M pH6 phosphate buffer and is recentrifuged adescribed above. The latter operation is carried out a second time inorder to effectively remove any residual substrate.

Warburg Method

The evaluation of the respiration of C. tropicalis on a polyacrylate iscarried out in Warburg flasks (total volume of 3 ml) comprising 1.3 mlof 0.1 M pH6 phosphate buffer, 1 ml of yeast suspension (about 3 mg dryweight) and 0.5 ml of polyacrylate at 1.12 g/l⁻¹ (final concentration of200 ppm).

Control tests are carried out in parallel:

-   -   a flask containing only phosphate buffer (2.8 ml) allows the        atmospheric pressure variations to be measured    -   the endogenous respiration is measured in a flask containing        only phosphate buffer (1.8 ml) and the yeast suspension (1 ml)    -   the respiration due to contaminants which may be present in the        acrylate solution is also evaluated by a test comprising the        acrylate (0.5 ml) and the phosphate buffer (2.3 ml).

The flasks are agitated in a water bath at 30° C.

Measurements of the pressure variations due to the appearance of CO₂,which is indicative of the metabolism of the acrylate by the yeast, arecarried out every 15 minutes.

Cultures of C. tropicalis on Polyacrylate

Two types of culture are carried out: cultures exclusively comprisingpolyacrylate as carbon source and cultures combining yeast extract. Thefirst case makes it possible to indicate the use of the compound by themicroorganism. The second case is directed towards optimizing this usein order to increase the degradation efficiency by promoting the growthof the yeast.

In both cases, these media comprise a conventional mineral medium(MgSO₄.7H₂O g; CaCl₂ 2H₂O 0.1 g: NaCl 1 g; FeSO₄.7H₂O 0.1 g; ZnSO₄.7H₂O0.1 g; CoCl₂ 0.1 g; CuSO₄.5H₂O 10 mg; AlK (SO₄)₂.12H₂O 10 mg; H₃BO₃ 10mg; Na₂MoO₄.2H₂O 2 mg; qs 1 l distilled water) combined with 0.1 M pH6phosphate buffer in proportions of 2/98. The polyacrylate is at a finalconcentration of 500 ppm.

The yeast extract which may be added has a final concentration of 200ppm this concentration may be increased up to 500 ppm if the growthremains too little. The flasks are incubated at 30° C. with transverseagitation and are subculture after one week. The cultures are thencontinued for 15 days under the same conditions.

Evaluation of the Calcium-complexing Ability

The principle of this test consists in measuring the ability of a givenpolymer to prevent the formation of a precipitate of CaSO₄ from sodiumsulphate and calcium chloride.

The protocol used is as follows:

Two aqueous solutions are prepared starting with distilled water, tocontain the following salts:

Solution A: CaCl₂.2H₂O 64.9 g/l + MgCl₂ 0.5 g/l Solution B: Na₂SO₄ 62.7g/l

400 ml of distilled water are introduced into a 500 ml flask and 50 mlof solution A is gradually added thereto, with agitation, followed by 50ml of solution B. In a flask serving as control, nothing else is added,while a certain amount of antitartar agent is added to the other twoflasks. At time t=0, after homogenization of the solutions, a few ml ofsolution are taken and the calcium and magnesium therein are assayed.The flasks are stoppered and then left to stand for 7 days. A few ml ofsupernatant liquid are then taken and the calcium and magnesium arere-assayed.

The ion concentration is measured by emission spectrometry using the ICP(Inductively Coupled Plasma) technique.

The results obtained are expressed as ppm of calcium in the solutions attime 0 and after 7 days of contact.

The examples which follow illustrate the invention without limiting itsscope.

EXAMPLE 1 (COMPARATIVE)

Acrylic Acid (AA)/Vinyl Monomers Copolymer in Solvent Phase

50 ml of tetrahydrofuran (THF), 5.76 g of acrylic acid, 0.98 g of maleicanhydride, 2 g of ethylene glycol vinyl ether (EGVE) and 0.296 g ofazo-bis-isobutyronitrile (AIBN) are introduced into a 100 ml two-neckedround-bottomed flask fitted with a condenser and a nitrogen inlet.

The reaction mixture is degassed by a succession of vacuum and nitrogencycles and is then placed in an oil bath thermostatically maintained at70° C.

After reaction for 12 hours the reaction mixture is concentrated on arotary evaporator and then precipitated (twice) filtered (sinter 5) anddried in an oven under vacuum (5×10⁻² bar) for a minimum of six hours.

Results Transfer Ref. Composition T° C. agent Initiator I₁₀₀₀ BG 78AABO/AM10/EGVE10 68 (reflux) No AIBN 56Oxidative Degradability

Under the test conditions, the product obtained has a degradabilityindex I₁₀₀₀ of 56, this result being higher than that of the referencepolyacrylates, whose I₁₀₀₀ is between 18 and 26 under the sameconditions.

Similarly, a commercial copolymer of methyl vinyl ether and of maleicanhydride, Gantrez, has an I₁₀₀₀ of 46.5, which clearly confirms thebiodegradability of the polycarboxylic-vinyl copolymers.

Finally, a polyvinyl alcohol homopolymer with very good biodegradabilityhas an I₁₀₀₀ of 212.1, which may thus be considered as the upper limitunder the test conditions.

EXAMPLE 2

AA/Isoprene Copolymer in Solvent Phase

1. Batchwise Synthesis at the Reflux Point of the Solvent (68° C.)

20 ml of tetrahydrofuran, 2.88 g of acrylic acid, 0.68 g of isoprene,0.082 g of AIBN and 0.131 g of thioglycolic acid (TGA) as transferagent, if necessary, are introduced into a 100 ml Schlenck tube.

The reaction mixture is degassed by a succession of vacuum and nitrogencycles and is then placed in an oil bath thermostatically maintained at70° C.

After reaction for 12 hours, the reaction mixture is concentrated on arotary evaporator and then precipitated (twice), filtered (sinter 5) anddried in an oven under vacuum 5×10⁻² bar) for a minimum of six hours.

Two products were prepared according to this method. They have thereference numbers BG 70 and BG 115.

2. Semi-continuous Synthesis in a Reactor Under Pressure (70° C.; 2.5bar)

0.6 g of AIBN, 33.5 g of acrylic acid and 90 g of THF are introducedinto a 500 ml stainless-steel reactor able to withstand a minimumpressure of 5 bar, fitted with a magnetic stirring bar.

The reactor is hermetically closed by a lid with 8 screws, on which ismounted a manometer and a valve which can be used to introduce liquidsand to degas the reactor.

The pressure in the reactor is raised to 2.5 bar by introduction ofnitrogen.

7.5 g of isoprene and 180 g of THF are weighed into a flask,thermostatically maintained by an ice bath. The filled flask is placedon a balance to monitor the decrease in mass corresponding to the amountintroduced into the reactor. The flask is connected to a metering pump,which is itself connected to the reactor. The connecting tubes arepurged and the reactor is placed in an oil bath thermostaticallymaintained at 70° C. and stirred magnetically. There is a risk of thepressure increasing slightly: it should not exceed 5 bar. Introductionof the THF/isoprene mixture into the reactor is then commenced. Theaddition lasts 180 min and the reaction is maintained at 70° C. for afurther 17 hours.

At the end of the reaction, the reactor is placed in an ice bath inorder to reduce the internal pressure, and after 30 minutes it isdegassed.

The reaction mixture is concentrated on a rotary evaporator and thenprecipitated (twice), filtered (sinter 5) and dried in an oven undervacuum (5×10⁻² bar) for a minimum of six hours.

The product obtained has the reference number CL 56.

Results Transfer Ref. Composition T° C. agent Initiator I₁₀₀₀ BG 70AA80/Isopr20 68 No AIBN 48.6 (reflux) BC115 AA80/Isopr20 68 Yes AIBN62.4 (reflux) CL 56 AA80/Isopr20 70 No AIBN 50Oxidative Degradability

Under the test conditions, the products obtained have a degradabilityindex I₁₀₀₀ of between 48.6 and 68.4, this result being higher than thatof the reference polyacrylates, whose I₁₀₀₀ is between 18 and 26 underthe same conditions. This is confirmed in the presence or absence of atransfer agent. These results show that the degradability of this typeof copolymer in the oxidation test is of an entirely equivalent level tothat of the structures described in Example 1 corresponding to EP 0 4 97611.

Microbiological Degradability

The AA/isoprene copolymer (BG70) was moreover evaluated inmicrobiological degradation under the conditions described above. Twotypes of results were obtained.

a—Respiration Test

The copolymer was used as carbon substrate for Candida tropicaliscultures, compared with readily metabolized control glucose substrate,and with a reference polyacrylate.

The respiration values obtained are as follows:

Respiration, Reference Composition μl O₂/h.g of cells Glucose — 17.3BG70 AA80/Isoprene20 5.1 Norasol 4500 AA Homo- 0 polymer

Compared with a standard polyacrylate which causes no respiration, thecopolymer with isoprene has a specific respiration level of close to 30%of that of glucose, which indicates a marked improvement inbiodegradability.

b—Assimilation Test

The copolymer was used as carbon substrate for Candida tropicaliscultures of longer duration, and analyzed by liquid chromatographycomparatively, after culturing for 15 days.

The analysis of these results shows that about 72.5% of the copolymerwas degraded by the microorganism over the 15 days of culture. Washingof the biomass with saline solutions reveals no trace of polymer, whichis proof that biodegradation has taken place, rather than adsorption ofthe polymer thereon.

Complexation

The copolymers obtained are dissolved in 0.1 M sodium hydroxide beforeanalysis, and are then returned to the test pH. The level of calciummeasurable after 7 days of contact indicates the ability of the polymerevaluated to inhibit its precipitation in the form of CaSO₄. The tablebelow indicates that the effect persists up to 0.25 ppm of AA/isoprenecopolymer under the test conditions, and up to a similar value for thereference polyacrylate, whereas no effect is measured for the control.

Content of Content of Ca²⁺ ppm at Ca²⁺ ppm at Reference ppm t = 0 t = 7days BG70 0.05 2260 1590 0.25 2290 2290 0.5 2290 2270 Norasol 0.1 1860 890 4500 0.4 1780 1530 1 1790 1680 Control 1930  940

These results make it possible to conclude that the novel AA/isoprenepolymers show a power with respect to calcium which is equivalent tothat of a reference polyacrylate such as Norasol 4500.

1. A hydrophilic polymer with improved biodegradability, comprising:from 70% to 99% by weight of units derived by polymerization from atleast one monomers A bearing a carboxylic acid function or an equivalentfunction, from 1% to 30% by weight of units derived by polymerizationfrom at least one monomers B bearing an electron-rich group or afunction capable of introducing an electron-rich group into the mainchain, wherein monomers B is selected from the group consisting ofmonomers bearing two conjugated double bonds and monomers bearing atriple bond; and units derived by polymerization from at least onemonomers C which is copolymerizable with A and B, but is different fromA and B, the amount of such units being up to 29% by weight, whereinmonomers C is selected from the group consisting of vinyl, acrylic,styrene and derivatives thereof.
 2. The hydrophilic polymer as claimedin claim 1, wherein the monomers A is chosen from the group consistingof monomers bearing at least one carboxylic acid and derivativesthereof.
 3. The hydrophilic polymer as claimed in claim 1, wherein thehydrophilic polymer is crosslinked with a difunctional agent to form acarboxylic polymer which can be used as a superabsorbent.
 4. Thehydrophilic polymer as claimed in claim 2, wherein monomers A isselected from the group consisting of maleic anhydride, acrylic acid,methacrylic acid, itaconic acid, fumaric acid, maleic acid and the saltsof the foregoing.
 5. The hydrophilic polymer as claimed in claim 4,wherein the monomers A is acrylic acid.
 6. A hydrophilic polymer withimproved biodegradability, comprising: from 70% to 99% by weight ofunits derived by polymerization from at least one monomers A bearing acarboxylic acid function or an equivalent function, from 1% to 30% byweight of units derived by polymerization from at least one isoprene,and units derived by polymerization from at least one monomers C whichis copolymerizable with A and isoprene, but is different from A andisoprene, the amount of such units being up to 29% by weight.
 7. Thehydrophilic polymer as claimed in claim 6, wherein the monomers C isselected from the group consisting of vinyl, acrylic, styrene monomersand derivatives thereof.
 8. A hydrophilic polymer with improvedbiodegradability, comprising: from 70% to 99% by weight of units derivedby polymerization from at least one monomers A bearing a carboxylic acidfunction or an equivalent function, from 1% to 30% by weight of unitsderived by polymerization from at least one monomers B, wherein monomersB bears two conjugated double bonds and is selected from the groupconsisting of butadiene, isoprene, chloroprene, dimethylbutadienie,cyclohexadiene, butadienecarboxylic acid and butadienedicarboxylic acid,and units derived by polymerization from at least one monomers C whichis copolymerizable with A and B, but is different from A and B, theamount of such units being up to 29% by weight.
 9. A hydrophilic polymerwith improved biodegradability, comprising: from 70% to 99% by weight ofunits derived by polymerization from at least one monomers A bearing acarboxylic acid function or an equivalent function, from 1% to 30% byweight of units derived by polymerization from at least one monomers B,wherein monomers B bears a triple bond and is selected from the groupconsisting of acetylene, acetylenecarboxylic acid andacetylenedicarboxylic acid, and units derived by polymerization from atleast one monomers C which is copolymerizable with A and B, but isdifferent from A and B, the amount of such units being up to 29% byweight.
 10. The hydrophilic polymer as claimed in claim 8, wherein themonomers C is selected from the group consisting of vinyl, acrylic,styrene monomers and derivatives thereof.
 11. The hydrophilic polymer asclaimed in claim 9, wherein the monomers C is selected from the groupconsisting of vinyl, acrylic, styrene monomers and derivatives thereof.12. A detergent composition comprising the hydrophilic polymer ofclaim
 1. 13. A detergent composition comprising the hydrophilic polymerof claim
 6. 14. A detergent composition comprising the hydrophilicpolymer of claim
 8. 15. A detergent composition comprising thehydrophilic polymer of claim 9.